Ion mobility spectrometer

Abstract

An ion mobility spectrometer is disclosed wherein ions are passed through an ion mobility spectrometer ( 5 ) and become temporally separated. Ions having a relatively high ion mobility are transmitted by a non-destructive ion gate ( 6 ) but ions having a relatively low ion mobility are subsequently trapped within the ion mobility spectrometer ( 5 ) when the ion gate ( 6 ) is switched so as to prevent ions from being onwardly transmitted. Ions which are transmitted by the ion gate ( 6 ) are trapped in a downstream ion trap ( 7 ). The ions are then returned back upstream to a second upstream ion trap ( 4 ).

1. A method of mass spectrometry comprising:
 passing a first group of ions through an ion mobility spectrometer or separator in order to separate temporally at least some of said ions; 
 operating an ion gate so that ions having drift times within a time window T 1  are transmitted by said ion gate but ions having drift times outside of said time window T 1  are not transmitted by said ion gate; 
 passing at least some of said ions having drift times within said time window T 1  through said ion mobility spectrometer or separator again in order to separate temporally at least some of said ions; and 
 passing at least some or substantially all of said ions having drift times outside of said time window T 1  back through said ion mobility spectrometer or separator and storing said ions in a first upstream ion trap; wherein 
 prior to passing at least some of said ions having drift times within said time window T 1  through said ion mobility spectrometer or separator again said method further comprises the steps of: 
 trapping said ions having drift times within said time window T 1  in a downstream ion trap, passing said ions back upstream through said ion mobility spectrometer or separator, storing said ions in a second upstream ion trap and ejecting said ions from said second upstream ion trap into said ion mobility spectrometer or separator. 
 
     
     
       2. A method as claimed in  claim 1 , further comprising:
 operating said ion gate so that ions having drift times within a time window T 2  are transmitted by said ion gate but ions having drift times outside of said time window T 2  are not transmitted by said ion gate; 
 passing at least some or substantially all of said ions having drift times outside of said time window T 2  back through said ion mobility spectrometer or separator and storing said ions in a first upstream ion trap; and 
 trapping said ions having drift times within said time window T 2  in a downstream ion trap, passing said ions back upstream through said ion mobility spectrometer or separator, storing said ions in a second upstream ion trap, ejecting said ions from said second upstream ion trap into said ion mobility spectrometer or separator and passing at least some of said ions having drift times within said time window T 2  through said ion mobility spectrometer or separator again in order to separate temporally at least some of said ions. 
 
     
     
       3. A method as claimed in  claim 1 , further comprising:
 operating said ion gate so that ions having drift times within a time window T 3  are transmitted by said ion gate but ions having drift times outside of said time window T 3  are not transmitted by said ion gate; 
 passing at least some or substantially all of said ions having drift times outside of said time window T 3  back through said ion mobility spectrometer or separator and storing said ions in a first upstream ion trap; 
 trapping said ions having drift times within said time window T 3  in a downstream ion trap, passing said ions back upstream through said ion mobility spectrometer or separator, storing said ions in a second upstream ion trap, ejecting said ions from said second upstream ion trap into said ion mobility spectrometer or separator and passing at least some of said ions having drift times within said time window T 3  through said ion mobility spectrometer or separator again in order to separate temporally at least some of said ions; and optionally 
 mass analysing at least some of said ions which emerge from said ion mobility spectrometer or separator. 
 
     
     
       4. A method as claimed in  claim 2 , wherein said first time window T 1  or said second time window T 2  or said third time window T 3  are substantially the same or substantially different. 
     
     
       5. A method as claimed in  claim 1 , further comprising:
 ejecting at least some of said ions having drift times outside of said time windows T 1 , T 2  and T 3  from said first upstream ion trap into said ion mobility spectrometer or separator as a second group of ions. 
 
     
     
       6. A method as claimed in  claim 5 , further comprising:
 passing said second group of ions through said ion mobility spectrometer or separator in order to separate temporally at least some of said ions; 
 operating an ion gate so that ions having drift times within a time window T 4  are transmitted by said ion gate but ions having drift times outside of said time window T 4  are not transmitted by said ion gate; 
 passing at least some of said ions having drift times within said time window T 4  through said ion mobility spectrometer or separator again in order to separate temporally at least some of said ions; and optionally 
 passing at least some or substantially all of said ions having drift times outside of said time window T 4  back through said ion mobility spectrometer or separator and storing said ions in a first upstream ion trap. 
 
     
     
       7. A method as claimed in  claim 6 , wherein prior to passing at least some of said ions having drift times within said time window T 4  through said ion mobility spectrometer or separator again said method further comprises the steps of:
 trapping said ions having drift times within said time window T 4  in a downstream ion trap, passing said ions back upstream through said ion mobility spectrometer or separator, storing said ions in a second upstream ion trap and ejecting said ions from said second upstream ion trap into said ion mobility spectrometer or separator. 
 
     
     
       8. A method as claimed in  claim 6 , further comprising:
 operating said ion gate so that ions having drift times within a time window T 5  are transmitted by said ion gate but ions having drift times outside of said time window T 5  are not transmitted by said ion gate; 
 passing at least some or substantially all of said ions having drift times outside of said time window T 5  back through said ion mobility spectrometer or separator and storing said ions in a first upstream ion trap; and 
 trapping said ions having drift times within said time window T 5  in a downstream ion trap, passing said ions back upstream through said ion mobility spectrometer or separator, storing said ions in a second upstream ion trap, ejecting said ions from said second upstream ion trap into said ion mobility spectrometer or separator and passing at least some of said ions having drift times within said time window T 5  through said ion mobility spectrometer or separator again in order to separate temporally at least some of said ions. 
 
     
     
       9. A method as claimed in  claim 6 , further comprising:
 operating said ion gate so that ions having drift times within a time window T 6  are transmitted by said ion gate but ions having drift times outside of said time window T 6  are not transmitted by said ion gate; 
 passing at least some or substantially all of said ions having drift times outside of said time window T 6  back through said ion mobility spectrometer or separator and storing said ions in a first upstream ion trap; 
 trapping said ions having drift times within said time window T 6  in a downstream ion trap, passing said ions back upstream through said ion mobility spectrometer or separator, storing said ions in a second upstream ion trap, ejecting said ions from said second upstream ion trap into said ion mobility spectrometer or separator and passing at least some of said ions having drift times within said time window T 6  through said ion mobility spectrometer or separator again in order to separate temporally at least some of said ions; and optionally 
 mass analysing at least some of said ions which emerge from said ion mobility spectrometer or separator. 
 
     
     
       10. A method as claimed in  claims 6 , wherein either:
 (i) said time window T 4  and said time window T 5  and said time window T 6  are substantially the same; or 
 (ii) said time window T 4  and said time window T 5  and said time window T 6  are substantially different. 
 
     
     
       11. A method as claimed in  claims 6 , wherein either:
 (i) said time window T 4  and said time window T 5  and said time window T 6  are substantially different to said time window T 1  and said time window T 2  and said time window T 3 ; or 
 (ii) said time window T 4  and said time window T 5  and said time window T 6  are substantially the same as said time window T 1  and said time window T 2  and said time window T 3 . 
 
     
     
       12. A method as claimed in  claim 1 , further comprising obtaining an ion mobility spectrum corresponding substantially to a single ion species by:
 determining the mean drift time of ions through said ion mobility spectrometer or separator as a function of the maximum drift time of ions transmitted by said ion gate; 
 determining at least one time period during which said mean drift time remains substantially constant as a function of the maximum drift time of ions transmitted by said ion gate; and 
 forming a composite ion mobility spectrum by summing ion mobility data obtained during said time period. 
 
     
     
       13. A method as claimed in  claim 1 , wherein said ions having drift times within said time window T 1  or said time window T 2  or said time window T 3  or said time window T 4  or said time window T 5  or said time window T 6  are not substantially fragmented when entering and whilst being stored in said downstream ion trap or when entering and whilst being stored in said second upstream ion trap. 
     
     
       14. A method as claimed in  claim 1 , wherein said ions having drift times outside said time window T 1  or outside said time window T 2  or outside said time window T 3  or outside said time window T 4  or outside said time window T 5  or outside said time window T 6  are not substantially fragmented when entering and whilst being stored in said first upstream ion trap. 
     
     
       15. A mass spectrometer comprising:
 an ion mobility spectrometer or separator; 
 an ion gate arranged downstream of said ion mobility spectrometer or separator; and 
 a first ion trap arranged upstream of said ion mobility spectrometer or separator; 
 a second ion trap arranged upstream of said ion mobility spectrometer or separator; 
 a third ion trap arranged downstream of said ion mobility spectrometer or separator; and 
 a control system arranged and adapted: 
 (i) to cause a first group of ions to pass through said ion mobility spectrometer or separator in order to separate temporally at least some ions; 
 (ii) to operate said ion gate so that ions having drift times within a time window T 1  are transmitted by said ion gate but ions having drift times outside of said time window T 1  are not transmitted by said ion gate; 
 (iii) to cause at least some of said ions having drift times within said time window T 1  to pass through said ion mobility spectrometer or separator again in order to separate temporally at least some of said ions; and 
 (iv) to cause at least some or substantially all of said ions having drift times outside of said time window T 1  to pass back through said ion mobility spectrometer or separator and storing said ions in said first ion trap; wherein 
 prior to passing at least some of said ions having drift times within said time window T 1  through said ion mobility spectrometer or separator again said control system is arranged and adapted: 
 (v) to trap said ions having drift times within said time window T 1  in said third ion trap, to pass said ions back upstream through said ion mobility spectrometer or separator, to store said ions in said second ion trap and elect said ions from said second ion trap into said ion mobility spectrometer or separator.